The present invention relates to a positioning device such as a micrometer, and more particularly to a power driven micrometer.
The use of micrometers to move a platform, such as a microscope stage, a precise distance along one or two axes is well known. See, for example, U.S. Pat. Nos. 3,281,945 and 3,555,916. The face of the micrometer spindle or screw is generally flat, with the stage being spring loaded so that contact between the stage and micrometer is maintained as the spindle advances and retreats.
In a number of applications, it is desirable to be able to achieve a micrometer function using a motor drive. This is especially true when the object or workpiece to be positioned is in a remote or inaccessible location. Such power driven micrometers are also well known in the art. See, for example, U.S. Pat. Nos. 2,854,755; 2,995,738, and 3,289,310. Indeed, powered micrometers are known not only for the transverse positioning of a workpiece or stage, but also for the inclining or tilting thereof. See, for example, U.S. Pat. No. 3,270,423.
While generally satisfactory for their purpose, the known power driven micrometers have not proven to be totally satisfactory.
In all of the known power driven micrometers, the motor or other drive means is maintained in a fixed position along the spindle screw or motor shaft axis, while the rotation of the motor shaft or an appended screw means is utilized to effect the desired positioning. This is true regardless of whether the positioning is accomplished by means of the interaction of the micrometer spindle face against a spring-loaded workpiece or stage or whether the positioning is accomplished by means of an interaction between the screw means (secured to the motor shaft) and a nut which is displaced along the screw means axis in response to rotation of the shaft. For example, while the aforementioned U.S. Pat. No. 3,270,423 shows micrometers which are carried on a rotatable member, the position of each micrometer motor along the motor shaft axis of that micrometer is fixed.
In a conventional motor-driven micrometer, the motor shaft is not directly connected to the screw means, but rather the motor shaft is linked to the screw means via a flexible coupling which permits the unit to accommodate bearing run-out and other misalignments without binding. More specifically, the connection between the motor shaft and the screw means typically includes a spline intermediate the screw means and the flexible coupling to accommodate the longitudinal travel of the screw means relative to the flexible coupling and motor shaft. As the motor, motor shaft, flexible coupling, spline and screw means are all disposed along the motor shaft axis, it will be immediately appreciated that the very multitude of parts places a limitation on the degree of micrometer miniaturization available. Furthermore, the use of so many parts increase the difficulty and cost of both the manufacturing and maintenance.
Accordingly, it is an object of the present invention to provide a powered micrometer wherein the motor and screw means are secured together for travel as a unit along the motor shaft axis, without the use of any flexible coupling or spline intermediate the motor shaft and the screw means.
It is another object to provide such a powered micrometer which is capable of enhanced miniaturization due to an improved motor shaft/screw means coupling and which is easy and inexpensive to produce and maintain due to the use of fewer parts.